SO, a pull (I have a proper puller) and clean the chip and socket with ISOpropo and we are back in business with the blitter, it is a non atari blitter btw, the kind that exxos sells, so, wonder if this machine has had issues with a blitter in the past, or on later boards they were using generic blitters.
I don't think that Mega STE-s were shipped without blitter, since it was introduced 2 years earlier.
Considering EPROM programming - I guess that you should try another EPROM chip. Or maybe just to erase it little longer. Really, there is no such ROM content what is bugger - there are only 0-s and 1-s everywhere, and every combination (there is 2 power 1048576 of them
) can be programmed in EPROM without problem, when all is OK - EPROM and programmer device + PSU for it if needed.
Famous Schrodinger's cat hypothetical experiment says that cat is dead or alive until we open box and see condition of poor animal, which deserved better logic. Cat is always in some certain state - regardless from is observer able or not to see what the state is.